Construction and Working of Constant Mesh Gearbox

Constant Mesh Gearbox Construction and Working

Constant mesh gearbox diagram is shown in the below figure.

constant mesh gearbox layout
The general layout of Constant Mesh Gearbox
In this type of gearbox, all the gears of the main shaft are in constant mesh with the corresponding gears of the countershaft or layshaft.
Two dog clutches are provided on the main shaft i.e. one in between the clutch gear and the second gear, and the other between the first gear and the reverse gear.

The dog clutch can slide on the shaft and rotate with it. While all the gears on the countershaft are rigidly fixed with it.

As and when the left-hand dog clutch is made to slide to the left by means of the gear shift lever, it meshes with the clutch gear and the top speed gear is obtained. When the left-hand dog clutch meshes with the second gear, the second gear is obtained.

Similarly, by sliding the right-hand dog clutch to the left and right, the first speed gear and reverse gear are obtained respectively.

In this type of gearbox, all the gears are in constant mesh and hence for this reason, they are safe from being damaged and irritating grinding sound does not occur while engaging and disengaging.

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